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mariadb/sql/opt_sum.cc
Jorgen Loland 6da93b223b Bug#47280 - strange results from count(*) with order by multiple 
columns without where/group
                     
Simple SELECT with implicit grouping used to return many rows if
the query was ordered by the aggregated column in the SELECT
list. This was incorrect because queries with implicit grouping
should only return a single record.
                              
The problem was that when JOIN:exec() decided if execution needed
to handle grouping, it was assumed that sum_func_count==0 meant
that there were no aggregate functions in the query. This
assumption was not correct in JOIN::exec() because the aggregate
functions might have been optimized away during JOIN::optimize().
                  
The reason why queries without ordering behaved correctly was
that sum_func_count is only recalculated if the optimizer chooses
to use temporary tables (which it does in the ordered case).
Hence, non-ordered queries were correctly treated as grouped.
                  
The fix for this bug was to remove the assumption that
sum_func_count==0 means that there is no need for grouping. This
was done by introducing variable "bool implicit_grouping" in the
JOIN object.

mysql-test/r/func_group.result:
  Add test for BUG#47280
mysql-test/t/func_group.test:
  Add test for BUG#47280
sql/opt_sum.cc:
  Improve comment for opt_sum_query()
sql/sql_class.h:
  Add comment for variables in TMP_TABLE_PARAM
sql/sql_select.cc:
  Introduce and use variable implicit_grouping instead of (!group_list && sum_func_count) in places that need to test if grouping is required. Also added comments for: optimization of aggregate fields for implicitly grouped queries  (JOIN::optimize) and choice of end_select method (JOIN::execute)
sql/sql_select.h:
  Add variable implicit_grouping, which will be TRUE for queries that contain aggregate functions but no GROUP BY clause. Also added comment to sort_and_group variable.
2009-10-14 10:46:50 +02:00

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/* Copyright (C) 2000-2003 MySQL AB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/**
@file
Optimising of MIN(), MAX() and COUNT(*) queries without 'group by' clause
by replacing the aggregate expression with a constant.
Given a table with a compound key on columns (a,b,c), the following
types of queries are optimised (assuming the table handler supports
the required methods)
@verbatim
SELECT COUNT(*) FROM t1[,t2,t3,...]
SELECT MIN(b) FROM t1 WHERE a=const
SELECT MAX(c) FROM t1 WHERE a=const AND b=const
SELECT MAX(b) FROM t1 WHERE a=const AND b<const
SELECT MIN(b) FROM t1 WHERE a=const AND b>const
SELECT MIN(b) FROM t1 WHERE a=const AND b BETWEEN const AND const
SELECT MAX(b) FROM t1 WHERE a=const AND b BETWEEN const AND const
@endverbatim
Instead of '<' one can use '<=', '>', '>=' and '=' as well.
Instead of 'a=const' the condition 'a IS NULL' can be used.
If all selected fields are replaced then we will also remove all
involved tables and return the answer without any join. Thus, the
following query will be replaced with a row of two constants:
@verbatim
SELECT MAX(b), MIN(d) FROM t1,t2
WHERE a=const AND b<const AND d>const
@endverbatim
(assuming a index for column d of table t2 is defined)
*/
#include "mysql_priv.h"
#include "sql_select.h"
static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref, Field* field,
COND *cond, uint *range_fl,
uint *key_prefix_length);
static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
COND *cond, uint range_fl, uint prefix_len);
static int maxmin_in_range(bool max_fl, Field* field, COND *cond);
/*
Get exact count of rows in all tables
SYNOPSIS
get_exact_records()
tables List of tables
NOTES
When this is called, we know all table handlers supports HA_HAS_RECORDS
or HA_STATS_RECORDS_IS_EXACT
RETURN
ULONGLONG_MAX Error: Could not calculate number of rows
# Multiplication of number of rows in all tables
*/
static ulonglong get_exact_record_count(TABLE_LIST *tables)
{
ulonglong count= 1;
for (TABLE_LIST *tl= tables; tl; tl= tl->next_leaf)
{
ha_rows tmp= tl->table->file->records();
if ((tmp == HA_POS_ERROR))
return ULONGLONG_MAX;
count*= tmp;
}
return count;
}
/**
Substitutes constants for some COUNT(), MIN() and MAX() functions.
@param tables list of leaves of join table tree
@param all_fields All fields to be returned
@param conds WHERE clause
@note
This function is only called for queries with sum functions and no
GROUP BY part. This means that the result set shall contain a single
row only
@retval
0 no errors
@retval
1 if all items were resolved
@retval
HA_ERR_KEY_NOT_FOUND on impossible conditions
@retval
HA_ERR_... if a deadlock or a lock wait timeout happens, for example
*/
int opt_sum_query(TABLE_LIST *tables, List<Item> &all_fields,COND *conds)
{
List_iterator_fast<Item> it(all_fields);
int const_result= 1;
bool recalc_const_item= 0;
ulonglong count= 1;
bool is_exact_count= TRUE, maybe_exact_count= TRUE;
table_map removed_tables= 0, outer_tables= 0, used_tables= 0;
table_map where_tables= 0;
Item *item;
int error;
if (conds)
where_tables= conds->used_tables();
/*
Analyze outer join dependencies, and, if possible, compute the number
of returned rows.
*/
for (TABLE_LIST *tl= tables; tl; tl= tl->next_leaf)
{
TABLE_LIST *embedded;
for (embedded= tl ; embedded; embedded= embedded->embedding)
{
if (embedded->on_expr)
break;
}
if (embedded)
/* Don't replace expression on a table that is part of an outer join */
{
outer_tables|= tl->table->map;
/*
We can't optimise LEFT JOIN in cases where the WHERE condition
restricts the table that is used, like in:
SELECT MAX(t1.a) FROM t1 LEFT JOIN t2 join-condition
WHERE t2.field IS NULL;
*/
if (tl->table->map & where_tables)
return 0;
}
else
used_tables|= tl->table->map;
/*
If the storage manager of 'tl' gives exact row count as part of
statistics (cheap), compute the total number of rows. If there are
no outer table dependencies, this count may be used as the real count.
Schema tables are filled after this function is invoked, so we can't
get row count
*/
if (!(tl->table->file->ha_table_flags() & HA_STATS_RECORDS_IS_EXACT) ||
tl->schema_table)
{
maybe_exact_count&= test(!tl->schema_table &&
(tl->table->file->ha_table_flags() &
HA_HAS_RECORDS));
is_exact_count= FALSE;
count= 1; // ensure count != 0
}
else
{
error= tl->table->file->info(HA_STATUS_VARIABLE | HA_STATUS_NO_LOCK);
if(error)
{
tl->table->file->print_error(error, MYF(0));
tl->table->in_use->fatal_error();
return error;
}
count*= tl->table->file->stats.records;
}
}
/*
Iterate through all items in the SELECT clause and replace
COUNT(), MIN() and MAX() with constants (if possible).
*/
while ((item= it++))
{
if (item->type() == Item::SUM_FUNC_ITEM)
{
Item_sum *item_sum= (((Item_sum*) item));
switch (item_sum->sum_func()) {
case Item_sum::COUNT_FUNC:
/*
If the expr in COUNT(expr) can never be null we can change this
to the number of rows in the tables if this number is exact and
there are no outer joins.
*/
if (!conds && !((Item_sum_count*) item)->get_arg(0)->maybe_null &&
!outer_tables && maybe_exact_count)
{
if (!is_exact_count)
{
if ((count= get_exact_record_count(tables)) == ULONGLONG_MAX)
{
/* Error from handler in counting rows. Don't optimize count() */
const_result= 0;
continue;
}
is_exact_count= 1; // count is now exact
}
((Item_sum_count*) item)->make_const((longlong) count);
recalc_const_item= 1;
}
else
const_result= 0;
break;
case Item_sum::MIN_FUNC:
{
/*
If MIN(expr) is the first part of a key or if all previous
parts of the key is found in the COND, then we can use
indexes to find the key.
*/
Item *expr=item_sum->get_arg(0);
if (expr->real_item()->type() == Item::FIELD_ITEM)
{
uchar key_buff[MAX_KEY_LENGTH];
TABLE_REF ref;
uint range_fl, prefix_len;
ref.key_buff= key_buff;
Item_field *item_field= (Item_field*) (expr->real_item());
TABLE *table= item_field->field->table;
/*
Look for a partial key that can be used for optimization.
If we succeed, ref.key_length will contain the length of
this key, while prefix_len will contain the length of
the beginning of this key without field used in MIN().
Type of range for the key part for this field will be
returned in range_fl.
*/
if (table->file->inited || (outer_tables & table->map) ||
!find_key_for_maxmin(0, &ref, item_field->field, conds,
&range_fl, &prefix_len))
{
const_result= 0;
break;
}
error= table->file->ha_index_init((uint) ref.key, 1);
if (!ref.key_length)
error= table->file->index_first(table->record[0]);
else
{
/*
Use index to replace MIN/MAX functions with their values
according to the following rules:
1) Insert the minimum non-null values where the WHERE clause still
matches, or
2) a NULL value if there are only NULL values for key_part_k.
3) Fail, producing a row of nulls
Implementation: Read the smallest value using the search key. If
the interval is open, read the next value after the search
key. If read fails, and we're looking for a MIN() value for a
nullable column, test if there is an exact match for the key.
*/
if (!(range_fl & NEAR_MIN))
/*
Closed interval: Either The MIN argument is non-nullable, or
we have a >= predicate for the MIN argument.
*/
error= table->file->index_read_map(table->record[0],
ref.key_buff,
make_prev_keypart_map(ref.key_parts),
HA_READ_KEY_OR_NEXT);
else
{
/*
Open interval: There are two cases:
1) We have only MIN() and the argument column is nullable, or
2) there is a > predicate on it, nullability is irrelevant.
We need to scan the next bigger record first.
*/
error= table->file->index_read_map(table->record[0],
ref.key_buff,
make_prev_keypart_map(ref.key_parts),
HA_READ_AFTER_KEY);
/*
If the found record is outside the group formed by the search
prefix, or there is no such record at all, check if all
records in that group have NULL in the MIN argument
column. If that is the case return that NULL.
Check if case 1 from above holds. If it does, we should read
the skipped tuple.
*/
if (item_field->field->real_maybe_null() &&
ref.key_buff[prefix_len] == 1 &&
/*
Last keypart (i.e. the argument to MIN) is set to NULL by
find_key_for_maxmin only if all other keyparts are bound
to constants in a conjunction of equalities. Hence, we
can detect this by checking only if the last keypart is
NULL.
*/
(error == HA_ERR_KEY_NOT_FOUND ||
key_cmp_if_same(table, ref.key_buff, ref.key, prefix_len)))
{
DBUG_ASSERT(item_field->field->real_maybe_null());
error= table->file->index_read_map(table->record[0],
ref.key_buff,
make_prev_keypart_map(ref.key_parts),
HA_READ_KEY_EXACT);
}
}
}
/* Verify that the read tuple indeed matches the search key */
if (!error && reckey_in_range(0, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
if (table->key_read)
{
table->key_read= 0;
table->file->extra(HA_EXTRA_NO_KEYREAD);
}
table->file->ha_index_end();
if (error)
{
if (error == HA_ERR_KEY_NOT_FOUND || error == HA_ERR_END_OF_FILE)
return HA_ERR_KEY_NOT_FOUND; // No rows matching WHERE
/* HA_ERR_LOCK_DEADLOCK or some other error */
table->file->print_error(error, MYF(0));
return(error);
}
removed_tables|= table->map;
}
else if (!expr->const_item() || !is_exact_count)
{
/*
The optimization is not applicable in both cases:
(a) 'expr' is a non-constant expression. Then we can't
replace 'expr' by a constant.
(b) 'expr' is a costant. According to ANSI, MIN/MAX must return
NULL if the query does not return any rows. Thus, if we are not
able to determine if the query returns any rows, we can't apply
the optimization and replace MIN/MAX with a constant.
*/
const_result= 0;
break;
}
if (!count)
{
/* If count == 0, then we know that is_exact_count == TRUE. */
((Item_sum_min*) item_sum)->clear(); /* Set to NULL. */
}
else
((Item_sum_min*) item_sum)->reset(); /* Set to the constant value. */
((Item_sum_min*) item_sum)->make_const();
recalc_const_item= 1;
break;
}
case Item_sum::MAX_FUNC:
{
/*
If MAX(expr) is the first part of a key or if all previous
parts of the key is found in the COND, then we can use
indexes to find the key.
*/
Item *expr=item_sum->get_arg(0);
if (expr->real_item()->type() == Item::FIELD_ITEM)
{
uchar key_buff[MAX_KEY_LENGTH];
TABLE_REF ref;
uint range_fl, prefix_len;
ref.key_buff= key_buff;
Item_field *item_field= (Item_field*) (expr->real_item());
TABLE *table= item_field->field->table;
/*
Look for a partial key that can be used for optimization.
If we succeed, ref.key_length will contain the length of
this key, while prefix_len will contain the length of
the beginning of this key without field used in MAX().
Type of range for the key part for this field will be
returned in range_fl.
*/
if (table->file->inited || (outer_tables & table->map) ||
!find_key_for_maxmin(1, &ref, item_field->field, conds,
&range_fl, &prefix_len))
{
const_result= 0;
break;
}
error= table->file->ha_index_init((uint) ref.key, 1);
if (!ref.key_length)
error= table->file->index_last(table->record[0]);
else
error= table->file->index_read_map(table->record[0], key_buff,
make_prev_keypart_map(ref.key_parts),
range_fl & NEAR_MAX ?
HA_READ_BEFORE_KEY :
HA_READ_PREFIX_LAST_OR_PREV);
if (!error && reckey_in_range(1, &ref, item_field->field,
conds, range_fl, prefix_len))
error= HA_ERR_KEY_NOT_FOUND;
if (table->key_read)
{
table->key_read=0;
table->file->extra(HA_EXTRA_NO_KEYREAD);
}
table->file->ha_index_end();
if (error)
{
if (error == HA_ERR_KEY_NOT_FOUND || error == HA_ERR_END_OF_FILE)
return HA_ERR_KEY_NOT_FOUND; // No rows matching WHERE
/* HA_ERR_LOCK_DEADLOCK or some other error */
table->file->print_error(error, MYF(0));
table->in_use->fatal_error();
return(error);
}
removed_tables|= table->map;
}
else if (!expr->const_item() || !is_exact_count)
{
/*
The optimization is not applicable in both cases:
(a) 'expr' is a non-constant expression. Then we can't
replace 'expr' by a constant.
(b) 'expr' is a costant. According to ANSI, MIN/MAX must return
NULL if the query does not return any rows. Thus, if we are not
able to determine if the query returns any rows, we can't apply
the optimization and replace MIN/MAX with a constant.
*/
const_result= 0;
break;
}
if (!count)
{
/* If count != 1, then we know that is_exact_count == TRUE. */
((Item_sum_max*) item_sum)->clear(); /* Set to NULL. */
}
else
((Item_sum_max*) item_sum)->reset(); /* Set to the constant value. */
((Item_sum_max*) item_sum)->make_const();
recalc_const_item= 1;
break;
}
default:
const_result= 0;
break;
}
}
else if (const_result)
{
if (recalc_const_item)
item->update_used_tables();
if (!item->const_item())
const_result= 0;
}
}
/*
If we have a where clause, we can only ignore searching in the
tables if MIN/MAX optimisation replaced all used tables
We do not use replaced values in case of:
SELECT MIN(key) FROM table_1, empty_table
removed_tables is != 0 if we have used MIN() or MAX().
*/
if (removed_tables && used_tables != removed_tables)
const_result= 0; // We didn't remove all tables
return const_result;
}
/**
Test if the predicate compares a field with constants.
@param func_item Predicate item
@param[out] args Here we store the field followed by constants
@param[out] inv_order Is set to 1 if the predicate is of the form
'const op field'
@retval
0 func_item is a simple predicate: a field is compared with
constants
@retval
1 Otherwise
*/
bool simple_pred(Item_func *func_item, Item **args, bool *inv_order)
{
Item *item;
*inv_order= 0;
switch (func_item->argument_count()) {
case 0:
/* MULT_EQUAL_FUNC */
{
Item_equal *item_equal= (Item_equal *) func_item;
Item_equal_iterator it(*item_equal);
args[0]= it++;
if (it++)
return 0;
if (!(args[1]= item_equal->get_const()))
return 0;
}
break;
case 1:
/* field IS NULL */
item= func_item->arguments()[0];
if (item->type() != Item::FIELD_ITEM)
return 0;
args[0]= item;
break;
case 2:
/* 'field op const' or 'const op field' */
item= func_item->arguments()[0];
if (item->type() == Item::FIELD_ITEM)
{
args[0]= item;
item= func_item->arguments()[1];
if (!item->const_item())
return 0;
args[1]= item;
}
else if (item->const_item())
{
args[1]= item;
item= func_item->arguments()[1];
if (item->type() != Item::FIELD_ITEM)
return 0;
args[0]= item;
*inv_order= 1;
}
else
return 0;
break;
case 3:
/* field BETWEEN const AND const */
item= func_item->arguments()[0];
if (item->type() == Item::FIELD_ITEM)
{
args[0]= item;
for (int i= 1 ; i <= 2; i++)
{
item= func_item->arguments()[i];
if (!item->const_item())
return 0;
args[i]= item;
}
}
else
return 0;
}
return 1;
}
/**
Check whether a condition matches a key to get {MAX|MIN}(field):.
For the index specified by the keyinfo parameter, index that
contains field as its component (field_part), the function
checks whether the condition cond is a conjunction and all its
conjuncts referring to the columns of the same table as column
field are one of the following forms:
- f_i= const_i or const_i= f_i or f_i is null,
where f_i is part of the index
- field {<|<=|>=|>|=} const or const {<|<=|>=|>|=} field
- field between const1 and const2
@param[in] max_fl Set to 1 if we are optimising MAX()
@param[in,out] ref Reference to the structure we store the key
value
@param[in] keyinfo Reference to the key info
@param[in] field_part Pointer to the key part for the field
@param[in] cond WHERE condition
@param[in,out] key_part_used Map of matchings parts
@param[in,out] range_fl Says whether including key will be used
@param[out] prefix_len Length of common key part for the range
where MAX/MIN is searched for
@retval
0 Index can't be used.
@retval
1 We can use index to get MIN/MAX value
*/
static bool matching_cond(bool max_fl, TABLE_REF *ref, KEY *keyinfo,
KEY_PART_INFO *field_part, COND *cond,
key_part_map *key_part_used, uint *range_fl,
uint *prefix_len)
{
if (!cond)
return 1;
Field *field= field_part->field;
if (!(cond->used_tables() & field->table->map))
{
/* Condition doesn't restrict the used table */
return 1;
}
if (cond->type() == Item::COND_ITEM)
{
if (((Item_cond*) cond)->functype() == Item_func::COND_OR_FUNC)
return 0;
/* AND */
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
Item *item;
while ((item= li++))
{
if (!matching_cond(max_fl, ref, keyinfo, field_part, item,
key_part_used, range_fl, prefix_len))
return 0;
}
return 1;
}
if (cond->type() != Item::FUNC_ITEM)
return 0; // Not operator, can't optimize
bool eq_type= 0; // =, <=> or IS NULL
bool noeq_type= 0; // < or >
bool less_fl= 0; // < or <=
bool is_null= 0;
bool between= 0;
switch (((Item_func*) cond)->functype()) {
case Item_func::ISNULL_FUNC:
is_null= 1; /* fall through */
case Item_func::EQ_FUNC:
case Item_func::EQUAL_FUNC:
eq_type= 1;
break;
case Item_func::LT_FUNC:
noeq_type= 1; /* fall through */
case Item_func::LE_FUNC:
less_fl= 1;
break;
case Item_func::GT_FUNC:
noeq_type= 1; /* fall through */
case Item_func::GE_FUNC:
break;
case Item_func::BETWEEN:
between= 1;
break;
case Item_func::MULT_EQUAL_FUNC:
eq_type= 1;
break;
default:
return 0; // Can't optimize function
}
Item *args[3];
bool inv;
/* Test if this is a comparison of a field and constant */
if (!simple_pred((Item_func*) cond, args, &inv))
return 0;
if (inv && !eq_type)
less_fl= 1-less_fl; // Convert '<' -> '>' (etc)
/* Check if field is part of the tested partial key */
uchar *key_ptr= ref->key_buff;
KEY_PART_INFO *part;
for (part= keyinfo->key_part; ; key_ptr+= part++->store_length)
{
if (part > field_part)
return 0; // Field is beyond the tested parts
if (part->field->eq(((Item_field*) args[0])->field))
break; // Found a part of the key for the field
}
bool is_field_part= part == field_part;
if (!(is_field_part || eq_type))
return 0;
key_part_map org_key_part_used= *key_part_used;
if (eq_type || between || max_fl == less_fl)
{
uint length= (key_ptr-ref->key_buff)+part->store_length;
if (ref->key_length < length)
{
/* Ultimately ref->key_length will contain the length of the search key */
ref->key_length= length;
ref->key_parts= (part - keyinfo->key_part) + 1;
}
if (!*prefix_len && part+1 == field_part)
*prefix_len= length;
if (is_field_part && eq_type)
*prefix_len= ref->key_length;
*key_part_used|= (key_part_map) 1 << (part - keyinfo->key_part);
}
if (org_key_part_used != *key_part_used ||
(is_field_part &&
(between || eq_type || max_fl == less_fl) && !cond->val_int()))
{
/*
It's the first predicate for this part or a predicate of the
following form that moves upper/lower bounds for max/min values:
- field BETWEEN const AND const
- field = const
- field {<|<=} const, when searching for MAX
- field {>|>=} const, when searching for MIN
*/
if (is_null)
{
part->field->set_null();
*key_ptr= (uchar) 1;
}
else
{
store_val_in_field(part->field, args[between && max_fl ? 2 : 1],
CHECK_FIELD_IGNORE);
if (part->null_bit)
*key_ptr++= (uchar) test(part->field->is_null());
part->field->get_key_image(key_ptr, part->length, Field::itRAW);
}
if (is_field_part)
{
if (between || eq_type)
*range_fl&= ~(NO_MAX_RANGE | NO_MIN_RANGE);
else
{
*range_fl&= ~(max_fl ? NO_MAX_RANGE : NO_MIN_RANGE);
if (noeq_type)
*range_fl|= (max_fl ? NEAR_MAX : NEAR_MIN);
else
*range_fl&= ~(max_fl ? NEAR_MAX : NEAR_MIN);
}
}
}
else if (eq_type)
{
if ((!is_null && !cond->val_int()) ||
(is_null && !test(part->field->is_null())))
return 0; // Impossible test
}
else if (is_field_part)
*range_fl&= ~(max_fl ? NO_MIN_RANGE : NO_MAX_RANGE);
return 1;
}
/**
Check whether we can get value for {max|min}(field) by using a key.
If where-condition is not a conjunction of 0 or more conjuct the
function returns false, otherwise it checks whether there is an
index including field as its k-th component/part such that:
-# for each previous component f_i there is one and only one conjunct
of the form: f_i= const_i or const_i= f_i or f_i is null
-# references to field occur only in conjucts of the form:
field {<|<=|>=|>|=} const or const {<|<=|>=|>|=} field or
field BETWEEN const1 AND const2
-# all references to the columns from the same table as column field
occur only in conjucts mentioned above.
-# each of k first components the index is not partial, i.e. is not
defined on a fixed length proper prefix of the field.
If such an index exists the function through the ref parameter
returns the key value to find max/min for the field using the index,
the length of first (k-1) components of the key and flags saying
how to apply the key for the search max/min value.
(if we have a condition field = const, prefix_len contains the length
of the whole search key)
@param[in] max_fl 0 for MIN(field) / 1 for MAX(field)
@param[in,out] ref Reference to the structure we store the key value
@param[in] field Field used inside MIN() / MAX()
@param[in] cond WHERE condition
@param[out] range_fl Bit flags for how to search if key is ok
@param[out] prefix_len Length of prefix for the search range
@note
This function may set table->key_read to 1, which must be reset after
index is used! (This can only happen when function returns 1)
@retval
0 Index can not be used to optimize MIN(field)/MAX(field)
@retval
1 Can use key to optimize MIN()/MAX().
In this case ref, range_fl and prefix_len are updated
*/
static bool find_key_for_maxmin(bool max_fl, TABLE_REF *ref,
Field* field, COND *cond,
uint *range_fl, uint *prefix_len)
{
if (!(field->flags & PART_KEY_FLAG))
return 0; // Not key field
TABLE *table= field->table;
uint idx= 0;
KEY *keyinfo,*keyinfo_end;
for (keyinfo= table->key_info, keyinfo_end= keyinfo+table->s->keys ;
keyinfo != keyinfo_end;
keyinfo++,idx++)
{
KEY_PART_INFO *part,*part_end;
key_part_map key_part_to_use= 0;
/*
Perform a check if index is not disabled by ALTER TABLE
or IGNORE INDEX.
*/
if (!table->keys_in_use_for_query.is_set(idx))
continue;
uint jdx= 0;
*prefix_len= 0;
for (part= keyinfo->key_part, part_end= part+keyinfo->key_parts ;
part != part_end ;
part++, jdx++, key_part_to_use= (key_part_to_use << 1) | 1)
{
if (!(table->file->index_flags(idx, jdx, 0) & HA_READ_ORDER))
return 0;
/* Check whether the index component is partial */
Field *part_field= table->field[part->fieldnr-1];
if ((part_field->flags & BLOB_FLAG) ||
part->length < part_field->key_length())
break;
if (field->eq(part->field))
{
ref->key= idx;
ref->key_length= 0;
ref->key_parts= 0;
key_part_map key_part_used= 0;
*range_fl= NO_MIN_RANGE | NO_MAX_RANGE;
if (matching_cond(max_fl, ref, keyinfo, part, cond,
&key_part_used, range_fl, prefix_len) &&
!(key_part_to_use & ~key_part_used))
{
if (!max_fl && key_part_used == key_part_to_use && part->null_bit)
{
/*
The query is on this form:
SELECT MIN(key_part_k)
FROM t1
WHERE key_part_1 = const and ... and key_part_k-1 = const
If key_part_k is nullable, we want to find the first matching row
where key_part_k is not null. The key buffer is now {const, ...,
NULL}. This will be passed to the handler along with a flag
indicating open interval. If a tuple is read that does not match
these search criteria, an attempt will be made to read an exact
match for the key buffer.
*/
/* Set the first byte of key_part_k to 1, that means NULL */
ref->key_buff[ref->key_length]= 1;
ref->key_length+= part->store_length;
ref->key_parts++;
DBUG_ASSERT(ref->key_parts == jdx+1);
*range_fl&= ~NO_MIN_RANGE;
*range_fl|= NEAR_MIN; // Open interval
}
/*
The following test is false when the key in the key tree is
converted (for example to upper case)
*/
if (field->part_of_key.is_set(idx))
{
table->key_read= 1;
table->file->extra(HA_EXTRA_KEYREAD);
}
return 1;
}
}
}
}
return 0;
}
/**
Check whether found key is in range specified by conditions.
@param[in] max_fl 0 for MIN(field) / 1 for MAX(field)
@param[in] ref Reference to the key value and info
@param[in] field Field used the MIN/MAX expression
@param[in] cond WHERE condition
@param[in] range_fl Says whether there is a condition to to be checked
@param[in] prefix_len Length of the constant part of the key
@retval
0 ok
@retval
1 WHERE was not true for the found row
*/
static int reckey_in_range(bool max_fl, TABLE_REF *ref, Field* field,
COND *cond, uint range_fl, uint prefix_len)
{
if (key_cmp_if_same(field->table, ref->key_buff, ref->key, prefix_len))
return 1;
if (!cond || (range_fl & (max_fl ? NO_MIN_RANGE : NO_MAX_RANGE)))
return 0;
return maxmin_in_range(max_fl, field, cond);
}
/**
Check whether {MAX|MIN}(field) is in range specified by conditions.
@param[in] max_fl 0 for MIN(field) / 1 for MAX(field)
@param[in] field Field used the MIN/MAX expression
@param[in] cond WHERE condition
@retval
0 ok
@retval
1 WHERE was not true for the found row
*/
static int maxmin_in_range(bool max_fl, Field* field, COND *cond)
{
/* If AND/OR condition */
if (cond->type() == Item::COND_ITEM)
{
List_iterator_fast<Item> li(*((Item_cond*) cond)->argument_list());
Item *item;
while ((item= li++))
{
if (maxmin_in_range(max_fl, field, item))
return 1;
}
return 0;
}
if (cond->used_tables() != field->table->map)
return 0;
bool less_fl= 0;
switch (((Item_func*) cond)->functype()) {
case Item_func::BETWEEN:
return cond->val_int() == 0; // Return 1 if WHERE is false
case Item_func::LT_FUNC:
case Item_func::LE_FUNC:
less_fl= 1;
case Item_func::GT_FUNC:
case Item_func::GE_FUNC:
{
Item *item= ((Item_func*) cond)->arguments()[1];
/* In case of 'const op item' we have to swap the operator */
if (!item->const_item())
less_fl= 1-less_fl;
/*
We only have to check the expression if we are using an expression like
SELECT MAX(b) FROM t1 WHERE a=const AND b>const
not for
SELECT MAX(b) FROM t1 WHERE a=const AND b<const
*/
if (max_fl != less_fl)
return cond->val_int() == 0; // Return 1 if WHERE is false
return 0;
}
case Item_func::EQ_FUNC:
case Item_func::EQUAL_FUNC:
break;
default: // Keep compiler happy
DBUG_ASSERT(1); // Impossible
break;
}
return 0;
}
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